I think I've got it now. When there is a slow leak in the system it causes a reduce oil level in the reservoir/gearbox (which is where the oil level sensor is). The remaining oil is still "transiting through" the reservoir/gearbox but not hanging around long enough to give a meaningful reading. Thus the lubrication system is still operating with a much reduced indicated oil level. So it's really a case of "partial oil loss" as clearly with a total oil loss there would be no oil to lubricate the bearings at all. I wouldn't expect the situation to last that long,eventually the oil would leak away to a point where lubrication would end. this ties up neatly with RMC's statement "Our company does not have a procedure for monitoring secondary instruments ( oil quantity, pressure and temperature on the basis that " if it becomes critical the aircraft will tell us" :ok:

Thanks CCA, that was what I was looking for so your partial oil loss was not instantaneous and would have been picked up by bringing up the secondary instruments display. On the Trent 800 this low quantity indication does not pop up until almost 75% of INDICATED oil has gone ( although that still leaves just over 40 imperial pints, a little over 50% of the TOTAL SYSTEM oil).
Really interested to hear how many others have had a similar experience to CCA AND / or any references which show how many times this has happened. Read that the Trent 900 had 15 oil leaks in one year.....but no indication how much oil was lost in these cases.

I have just read your post again, now that you have Edited it to read no indicated oil from its original total loss of oil you are correct. Rather than asking me to read the post maybe get it correct in the first place.

No harm done though Exup eh? It just proves that the Drivers and the Engineers need to be ever vigilant and use the correct terminology, how often can a single word change the context of a situation completely? :cool:

Ex up, The clarification was necessary, however are you happy that this is not an indication problem...it is an indication that most of the oil has leaked out?

I believe R-R Trent engines are similar to most other large turbofan engines with respect to their lube oil system. The engine bearing chambers are scavenged by a shaft driven pump located in the EMAD gearbox, which is mounted to the lower section of the fan case. After the scavenged oil is de-aerated, it is returned to the oil tank. The Trent oil tank is separate from the EMAD gearbox housing and is mounted higher up on the fan case. It is the gray thing just to the right of the large vertical yellow cylinder in this picture.

The engine oil feed is provided by a shaft driven pressure pump located in the EMAD gearbox. The pressure pump is fed from the oil tank. The pressurized oil passes thru a filter and heat exchanger before being distributed to the engine bearings/gears/splines/carbon face seals, EMAD bearings/gears/splines/shaft seals, etc.

The oil level sensor is located in the oil tank, but even if a properly functioning oil level sensor indicates zero oil level in the tank, there can still be a fair amount of oil still circulating through the system. It will just be in the form of an air/oil mixture. If we consider that a primary function of lube oil flow is to provide cooling of engine bearings, then even having an air/oil mist sprayed from the lube jets onto the bearings can help significantly. The rolling element shaft bearings in a turbofan engine are very high performance devices, and would quickly fail due to scuffing with a total absence of lube oil.

As for the pressure and temperature sensors in the lube oil circuit, they are calibrated for liquid oil flow. If the oil tank level was essentially zero, but the scavenge and pressure pumps continued to operate, there would still be some compressed air & oil mist flowing thru the circuit which would be detected by the pressure sensor. However, the pressure of an air/oil mixture coming from the pressure pump would be much lower than a flow of liquid oil.

A large turbofan engine like the Trent has some capability to continue operating for a brief period with loss of lube oil. But it could not operate for extended periods at full power with a loss of lube oil.

Must be a British thing! Look at Triumph motorcycles!
(they leaked so much the entire frame was filled with oil, you knew you had a buffer when checking the frame oil, because it could be completely gone, and still enough oil in the engine crankcase and transmission to run the beast, and yes, engine and transmission oil were the same)

CCA,


"RR* oil is held in the gearbox not in an oil tank". Close, but no banana. Assuming you are talking about the RB211-524G engine, it does in fact have an oil tank which is integral to and attached onto the front face of the High Speed External Gearbox at about the 6 to 8 o'clock position.


Many, many moons ago, a wise old flight instructor said to me...."know your aeroplane, but KNOW it's systems" and I have lived by that creed ever since. Anytime I see an engine cowl open with engineers under it, or engineers working in general, I join them and ask questions.


McHale. :)

Smoke Theory of Electricity - The Compass Adjuster

Positive ground depends upon proper circuit functioning, the transmission of negative ions by retention of the visible spectral manifestation known as "smoke". Smoke is the thing that makes electrical circuits work; we know this to be true because every time one lets the smoke out of the electrical system, it stops working. This can be verified repeatedly through empirical testing.

When, for example, the smoke escapes from an electrical component (i.e., say, a Lucas voltage regulator), it will be observed that the component stops working. The function of the wire harness is to carry the smoke from one device to another; when the wire harness "springs a leak", and lets all the smoke out of the system, nothing works afterwards. Starter motors were frowned upon in British Automobiles for some time, largely because they consume large quantities of smoke, requiring very large wires.

It has been noted that Lucas components are possibly more prone to electrical leakage than Bosch or generic Japanese electrics. Experts point out that this is because Lucas is British and all things British leak. British engines leak oil, shock absorbers, hydraulic forks and disk brakes leak fluid, British tires leak air and the British defense establishment leaks secrets...so, naturally, British electronics leak smoke.

(Author Unknown ):D:D:D

Cap'n-

There are some R-R commercial turbofan engines that have a lube oil tank integral with the EMAD gearbox housing. The BR710 is one such engine. If you look at this picture, the structure just to the lower right of the fan containment ring is the lube oil tank (the part with the ID plate attached to it). It is an integral part of the EMAD gearbox housing casting.

I am intimately familiar with this particular housing casting since I designed it back in 1993. Rolls-Royce wanted the EMAD gearbox main housing casting to be single piece with an integral tank and piping to minimize the potential for leaks and maximize reliability. The downside of this approach was the high cost of manufacturing such a very complex casting.

riff raff,


Many thanks for the info. I was merely pointing out to CCA that said engine does in fact have an oil tank.


McHale. :) :ok:

Cap'n-

Gotcha. Every turbofan engine I know of does indeed have at least one lube oil tank somewhere. In fact, I believe there are some engines that have two separate lube oil tanks. A primary tank located integral with the EMAD gearbox, and a supplementary tank remote from the EMAD. The remote tank is used to replenish the primary tank if it experiences a loss of oil.